Mercury distribution in the skin of beluga (Delphinapterus leucas) and narwhal (Monodon monoceros) from the Canadian Arctic and mercury burdens and excretion by moulting

Beluga and narwhal skin as a whole (in Inuktitut known as “muktuk”) is considered to be a delicacy by native Canadian and Greenland people. Individual strata of the skin, and muscle from 27 beluga from the western, and 20 narwhal from the eastern Canadian Arctic, were analyzed for mercury and the thickness and density of each skin layer was measured. Mercury was not uniformly distributed in the skin, but increased outwardly with each layer. The concentration was only 0.29 and 0.16 μg/g (wet wt) in the innermost layer (dermis) of belugas and narwhal respectively, and 1.5 and 1.4 μg/g (wet wt) in the outermost layer (degenerative epidermis) of beluga and narwhal, respectively. There was a significant (α = 0.05) association between age and mercury concentration in each skin layer, the regression coefficients progressively increasing from the inner layer (dermis) to the outer layer: 0.011-0.063 μg/g year− 1; 0.034 μg/g year− 1 for skin as a whole; 0.054 μg/g year− 1 for muscle. The concentration of total mercury was 0.84 and 0.59 μg/g (wet wt) in skin as a whole (muktuk) of beluga and narwhal respectively, and 0.12 and 0.03 μg/g in blubber, respectively. The average, total mercury concentration in muscle tissue was 1.4 and 0.81 μg/g wet wt, in beluga and narwhal respectively, exceeding (except for blubber) the Canadian Government's Guideline (0.5 μg/g wet wt) for fish export and consumption. The skin surface area of an average-size beluga and narwhal was estimated (6.10 and 6.50 m2, respectively), as were excretions of mercury through moulting (13,861 and 6721 μg year− 1; 14 and 7 mg year− 1) for belugas and narwhal, respectively. The whole-body mercury burden (699,300 μg; 700 mg) for a 1000 kg beluga and its various tissues were estimated, as was the fraction of mercury excreted by moulting (2-0.42% of the whole-body burden). Annual mercury burden increments in beluga skin, muscle and the whole body were estimated (2750; 17,280; 40,00 μg year− 1, respectively), using regression coefficients of age on mercury concentration. The annual gross mercury intake via food was estimated (131,400 μg), of which 70% was excreted.